<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <style>
       .flex-container {
            display: flex;
        }
       .fixed-width {
            width: 100px;
            background-color: lightblue;
        }
       .flex-item {
            flex: 1;
            background-color: lightgreen;
        }
    </style>
</head>
<body>
    <div class="flex-container">
        <div class="fixed-width">固定宽度100px</div>
        <div class="flex-item">flex: 1</div>
    </div>
</body>
</html>